In practice, it is known that the dynamic transfer of an axle load due to the acceleration or deceleration of a motor vehicle causes a change in the opposite sense in the momentary normal force on the front and rear axle. Because of the dependency of the tire cornering force on the normal force, the distribution of the lateral force between the front and the rear axle changes whereby a moment turning into the curve develops during deceleration and a moment turning out of the curve occurs when accelerating.
In correspondence therewith, it is also known in practice that, in certain driving conditions, the subjective feeling of the driver is that the motor vehicle is tilting forward over the front wheels, or is dipping over them such that at least one wheel frequently deflects to almost its maximum extent, as is the case for example when driving to the extreme in a curve or under heavy braking.
Particularly in the case of full braking, the motor vehicle tilts downwardly to a very great extent in the forward direction of travel as a consequence of the dynamic transfer of the axle load. The tires on the front axle are thereby extremely heavily loaded and thus are possibly no longer following linear operating points. At these operating points, the transmissible longitudinal and transverse forces are smaller than in the linear range. At the same time, the loading on the tires on the rear axle is substantially reduced and consequently they can only transfer low braking and cornering forces. Control of the vehicle as desired by the driver is then frequently no longer possible without systems for regulating the dynamics of the vehicle's movement.
The reduction in the load on the rear axle in the event of driving in a curve while applying full braking or in the event of driving rapidly or to the maximum extreme in a curve can be of such an extent that the rear wheel on the inner side of the curve lifts completely off the road and can no longer transfer any braking or lateral forces whatsoever. The front wheel on the outer side of the curve and also the rear wheel on the outer side of the curve are then frequently loaded in such a manner that they begin to slide so that the vehicle eventually breaks away.
In the context of the developments in integrated chassis control systems that have been known in practice up to now, (“integrated chassis control,” or “ICC”), one has sought to stabilize the motor vehicle in every conceivable driving situation by networking the essential systems for the dynamics of the vehicle's movement as one component of an interactive dynamic driving system (“interactive driving system,” or: “IDS”). Such systems for regulating the dynamics of the vehicle's movement and/or the electronic stability program (“electronic stability program,” or “ESP”) communicate with further control devices such as the brake assistant for example, whereby the respective items of data required for this purpose are transmitted over a data bus system (“controller area network,” or “CAN” bus). Hereby, the data can be transmitted over data bus systems of differing speeds in dependence on the importance thereof. Thus, for example, the time-sensitive signals in regard to the dynamics of the vehicle's movement are transmitted over a “high speed” data bus having a data transmission rate of at least 500 KB per second.
A dynamic transference of the axle load, such as occurs when the motor vehicle plunges over the front wheels, for example, can thus be detected more or less in real time and an electronic damping regulation process (“continuous damping control,” or “CDC”) can be activated, for example, in order to counteract the transfer of the axle load. Such expensive electronic damping control systems are, for example, based on shock absorbers controlled by solenoid valves whose characteristic can be continuously adapted to the road conditions, the vehicle movement, and the driving pattern in a stepless, precise and continuous manner in dependence on the prevailing data. Several acceleration sensors or the like can supply the signals required for optimal damping to the CDC control unit in combination with further signals from the CAN bus. The control unit calculates the requisite damping force for each wheel in real time, for example, by means of a characteristic diagram or the like. The adaptation of the shock absorbers can then take place within milliseconds. The vehicle bodywork can thus be kept steady; pitching motions when braking and bodywork movements when driving in curves or when driving over bumps are reduced to a noticeable extent.
Although the successes and improvements in regard to the dynamic transference of the axle load that can be attained thereby are indeed promising and have also proved satisfactory in practice, they are still inadequate for fully controlling a motor vehicle in every driving situation.